Textile materials, particularly those made from vegetable fibres such as cotton or linen and articles manufactured from them are generally washed by contacting the materials with a washing liquor containing the conventional detergent components such as soaps or synthetic detergents as well as builders of various kinds, alkaline salts and bleaching compounds.
In the most common method of treating textiles having bleachable stains, the liquor containing the textiles is heated from ambient temperature to a temperature close to that of boiling water, i.e. above 85.degree. C., and held at this temperature for some time before being cooled and the textiles withdrawn. At temperature of 85.degree. C. and above, the inorganic persalt bleaching compounds frequently incorporated in laundry detergents, i.e. sodium perborate and sodium percarbonate, have a high bleaching performance but this falls off rapidly at lower temperatures viz. at 70.degree. C. and below, so that the full benefit of the bleach is not obtained if the washing temperature is not high enough. Modern automatic washing machines are provided with programmed cycles that contain a heat-up stage to a temperature above 85.degree. C. (the so-called `boil wash`) but they include programmes for lower temperature washing cycles to handle coloured and synthetic fabrics. With the increasing incidence of use of these fabrics and the publicity accorded to energy conservation measures there is a tendency for the use of such lower temperature cycles to increase at the expense of the boil wash. Consequently there is a developing need for products having good bleaching ability in the temperature range of 70.degree. C. and below, both to maintain cleaning performance in the low temperature cycles and to make the most effective use of an expensive ingredient.
Bleaching agents which are effective at low temperatures have been known for many years, most being capable of releasing organic peracids as the bleaching species.
Examples of detergent compositions incorporating bleaching agents of this type are disclosed by Reichert et al U.S. Pat. No. 2,362,401 issued Nov. 7, 1944, Moyer U.S. Pat. No. 3,639,248 issued Feb. 1, 1972 and British Pat. Nos. 836,988 and 855,735.
These and other similar disclosures teach the incorporation of an organic precursor material into the formulation that reacts with the inorganic peroxy bleach component in the washing solution to give an organic peroxy bleach species, normally a peroxy acid. This peroxy bleach species is more effective in the lower temperature portions of the washing operation than the inorganic peroxy bleach. However products containing such combinations of organic peroxy compound precursors and inorganic peroxy bleaches have proved difficult to formulate for the reason that in the presence of moisture picked up during storage prior to use, these materials react to give the organic peroxy species which thereupon decomposes. This results in a lowered efficacy of the product.
Various methods have been proposed to achieve satisfactory stability of organic peroxy bleaching agents or of their precursors in detergent compositions, involving separate packaging as in Woods U.S. Pat. No. 3,532,634 issued Oct. 6, 1970: encapsulation as in Woods (supra), Lund & Neilsen U.S. Pat. No. 349,787 and Neilsen U.S. Pat. No. 3,494,786 both issued Feb. 10, 1970; coating as in Scheifer et al U.S. Pat. No. 3,441,507 issued Apr. 29, 1969; and granulation as in Moyer et al U.S. Pat. No. 3,639,248 issued Feb. 1, 1972. All of these methods are directed to the stabilisation of an organic peroxy bleaching agent or its precursor in a detergent product environment so as to provide the convenience of a single product, albeit with the limitation of the use of a fixed level of the bleaching species relative to the other detergent components on each occasion of use of the detergent. Attempts to improve the stability of the peroxy bleach or a precursor thereof in prior art compositions resulted in considerable inhibition of the release of the bleach into solution and thereby diminished effectiveness and increased cost.
Thus one disadvantage of the products of the prior art has been that they constitute costly formulations that lead to unnecessary and potentially damaging usage of bleach under certain circumstances.
A further disadvantage of the prior art products has been the difficulty of preventing fabric colour damage, particularly pin-point spotting, caused by direct contact of the textiles with undissolved particles of organic peroxy bleach per se and/or local concentrations or organic peroxy bleach in the immediate vicinity of precursor particles.
A yet further disadvantage associated with prior art products has been the potential for skin and internal tissue damage to humans arising from misuse or accidential ingestion under conditions in which reaction of the inorganic persalt and the organic percursor could occur to provide the highly reactive organic peroxy bleach species.
Accordingly one object of the present invention is the avoidance of these disadvantages by the incorporation of the bleaching agent precursor in an additive product in which the precursor is chemically and physically stable and is spatially separated from any inorganic peroxy bleach, the product being adapted for addition at any desired level to textile fabrics either before or during a washing operation in which conventional detergent compositions are employed. The present invention also seeks to maximise the effectiveness of the bleaching species by providing the bleaching agent precursor in a product form from which the precursor dissolves very rapidly into the aqueous washing liquor.
Another object of the invention is the provision of an additive product adapted to give enhanced bleachable stain removal particularly at temperatures of 70.degree. C. and below when added to a solution containing inorganic peroxy salts.